Yahoo is holding a free all day developer workshop at their headquarters in Sunnyvale, CA on September 29th, followed by a 24 hour hack-through-the night event.

We’ll kick things off on Friday, September 29th with a free all-day developer workshop. Then we’ll launch a 24-hour Hack Day with an outdoor party into the wee hours, with special guests providing the soundtrack. (Details to come later, but we guarantee this won’t be your usual corporate-wedding-band leading the crowd through 2am group sing-alongs of “Brick House.”) We’ll hack through the night, keep going through Saturday morning, and wind it all up that evening with hacker demos, judging from a panel of luminaries. and special awards for the coolest hacks. We’ll have special guest speakers all weekend, with Michael Arrington of TechCrunch presiding over the festivities. And after nightfall we’ll close things out with another round of entertainment that you would be happy to pay for, except that you won’t have to.

I’m a little too old to enjoy hacking through the night (it’s good to see the term “hacking” rescued from its conflation with “cracking,” though), but I’m sure lots of young and serious developers will attend.

So why are Yahoo! and Google, through its Summer of Code, wooing developers? For the same reasons that Microsoft and other software companies have been wooing developers for decades: to find prospective employees and build a qualified labor pool; to drive adoption of their platform at companies by influencing their IT staff; to encourage development of third party applications based on their platform and services.

This may be restating the obvious, but this event is one more sign that both Yahoo! and Google view themselves as software companies every bit as real and legitimate as Microsoft.